/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.server.reactive;

import org.apache.commons.logging.Log;
import org.reactivestreams.Publisher;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.PooledDataBuffer;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpLogging;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseCookie;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;
import java.util.stream.Collectors;

/**
 * Base class for {@link ServerHttpResponse} implementations.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @author Sebastien Deleuze
 * @author Brian Clozel
 * @since 5.0
 */
public abstract class AbstractServerHttpResponse implements ServerHttpResponse {

    protected final Log logger = HttpLogging.forLogName(getClass());
    private final DataBufferFactory dataBufferFactory;
    private final HttpHeaders headers;
    private final MultiValueMap<String, ResponseCookie> cookies;
    private final AtomicReference<State> state = new AtomicReference<>(State.NEW);
    private final List<Supplier<? extends Mono<Void>>> commitActions = new ArrayList<>(4);
    @Nullable
    private Integer statusCode;

    public AbstractServerHttpResponse(DataBufferFactory dataBufferFactory) {
        this(dataBufferFactory, new HttpHeaders());
    }


    public AbstractServerHttpResponse(DataBufferFactory dataBufferFactory, HttpHeaders headers) {
        Assert.notNull(dataBufferFactory, "DataBufferFactory must not be null");
        Assert.notNull(headers, "HttpHeaders must not be null");
        this.dataBufferFactory = dataBufferFactory;
        this.headers = headers;
        this.cookies = new LinkedMultiValueMap<>();
    }

    @Override
    public final DataBufferFactory bufferFactory() {
        return this.dataBufferFactory;
    }

    @Override
    public boolean setStatusCode(@Nullable HttpStatus status) {
        if (this.state.get() == State.COMMITTED) {
            return false;
        }
        else {
            this.statusCode = (status != null ? status.value() : null);
            return true;
        }
    }

    @Override
    @Nullable
    public HttpStatus getStatusCode() {
        return (this.statusCode != null ? HttpStatus.resolve(this.statusCode) : null);
    }

    /**
     * Return the HTTP status code of the response.
     *
     * @return the HTTP status as an integer value
     * @since 5.0.1
     */
    @Nullable
    public Integer getStatusCodeValue() {
        return this.statusCode;
    }

    /**
     * Set the HTTP status code of the response.
     *
     * @param statusCode the HTTP status as an integer value
     * @since 5.0.1
     */
    public void setStatusCodeValue(@Nullable Integer statusCode) {
        this.statusCode = statusCode;
    }

    @Override
    public HttpHeaders getHeaders() {
        return (this.state.get() == State.COMMITTED ?
                HttpHeaders.readOnlyHttpHeaders(this.headers) : this.headers);
    }

    @Override
    public MultiValueMap<String, ResponseCookie> getCookies() {
        return (this.state.get() == State.COMMITTED ?
                CollectionUtils.unmodifiableMultiValueMap(this.cookies) : this.cookies);
    }

    @Override
    public void addCookie(ResponseCookie cookie) {
        Assert.notNull(cookie, "ResponseCookie must not be null");

        if (this.state.get() == State.COMMITTED) {
            throw new IllegalStateException("Can't add the cookie " + cookie +
                    "because the HTTP response has already been committed");
        }
        else {
            getCookies().add(cookie.getName(), cookie);
        }
    }

    /**
     * Return the underlying server response.
     * <p><strong>Note:</strong> This is exposed mainly for internal framework
     * use such as WebSocket upgrades in the spring-webflux module.
     */
    public abstract <T> T getNativeResponse();

    @Override
    public void beforeCommit(Supplier<? extends Mono<Void>> action) {
        this.commitActions.add(action);
    }

    @Override
    public boolean isCommitted() {
        return this.state.get() != State.NEW;
    }

    @Override
    @SuppressWarnings("unchecked")
    public final Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
        // Write as Mono if possible as an optimization hint to Reactor Netty
        // ChannelSendOperator not necessary for Mono
        if (body instanceof Mono) {
            return ((Mono<? extends DataBuffer>) body).flatMap(buffer ->
                    doCommit(() -> writeWithInternal(Mono.just(buffer)))
                            .doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release));
        }
        return new ChannelSendOperator<>(body, inner -> doCommit(() -> writeWithInternal(inner)))
                .doOnError(t -> removeContentLength());
    }

    @Override
    public final Mono<Void> writeAndFlushWith(Publisher<? extends Publisher<? extends DataBuffer>> body) {
        return new ChannelSendOperator<>(body, inner -> doCommit(() -> writeAndFlushWithInternal(inner)))
                .doOnError(t -> removeContentLength());
    }

    private void removeContentLength() {
        if (!this.isCommitted()) {
            this.getHeaders().remove(HttpHeaders.CONTENT_LENGTH);
        }
    }

    @Override
    public Mono<Void> setComplete() {
        return !isCommitted() ? doCommit(null) : Mono.empty();
    }

    /**
     * A variant of {@link #doCommit(Supplier)} for a response without no body.
     *
     * @return a completion publisher
     */
    protected Mono<Void> doCommit() {
        return doCommit(null);
    }

    /**
     * Apply {@link #beforeCommit(Supplier) beforeCommit} actions, apply the
     * response status and headers/cookies, and write the response body.
     *
     * @param writeAction the action to write the response body (may be {@code null})
     * @return a completion publisher
     */
    protected Mono<Void> doCommit(@Nullable Supplier<? extends Mono<Void>> writeAction) {
        if (!this.state.compareAndSet(State.NEW, State.COMMITTING)) {
            return Mono.empty();
        }

        this.commitActions.add(() ->
                Mono.fromRunnable(() -> {
                    applyStatusCode();
                    applyHeaders();
                    applyCookies();
                    this.state.set(State.COMMITTED);
                }));

        if (writeAction != null) {
            this.commitActions.add(writeAction);
        }

        List<? extends Mono<Void>> actions = this.commitActions.stream()
                .map(Supplier::get).collect(Collectors.toList());

        return Flux.concat(actions).then();
    }

    /**
     * Write to the underlying the response.
     *
     * @param body the publisher to write with
     */
    protected abstract Mono<Void> writeWithInternal(Publisher<? extends DataBuffer> body);

    /**
     * Write to the underlying the response, and flush after each {@code Publisher<DataBuffer>}.
     *
     * @param body the publisher to write and flush with
     */
    protected abstract Mono<Void> writeAndFlushWithInternal(Publisher<? extends Publisher<? extends DataBuffer>> body);

    /**
     * Write the status code to the underlying response.
     * This method is called once only.
     */
    protected abstract void applyStatusCode();

    /**
     * Invoked when the response is getting committed allowing sub-classes to
     * make apply header values to the underlying response.
     * <p>Note that most sub-classes use an {@link HttpHeaders} instance that
     * wraps an adapter to the native response headers such that changes are
     * propagated to the underlying response on the go. That means this callback
     * is typically not used other than for specialized updates such as setting
     * the contentType or characterEncoding fields in a Servlet response.
     */
    protected abstract void applyHeaders();

    /**
     * Add cookies from {@link #getHeaders()} to the underlying response.
     * This method is called once only.
     */
    protected abstract void applyCookies();

    /**
     * COMMITTING -> COMMITTED is the period after doCommit is called but before
     * the response status and headers have been applied to the underlying
     * response during which time pre-commit actions can still make changes to
     * the response status and headers.
     */
    private enum State {NEW, COMMITTING, COMMITTED}

}
